This invention relates to a technology for enhancing controllability of output power based on a power control signal voltage of a high-frequency power amplifier circuit and gain's linear characteristics of a gain control amplifier, and particularly to a communication semiconductor integrated circuit device having a high-frequency power amplifier circuit built therein, and a technology effected if applied to a wireless communication system such as a cellular phone or the like with the communication semiconductor integrated circuit device built therein.
A high-frequency power amplifier circuit has been built in an output unit provided on the transmitting side of a wireless communication system (mobile communication system) such as a mobile phone, a cellular phone or the like. The high-frequency power amplifier circuit has a configuration wherein a semiconductor amplifying element corresponding to a final stage comprises a discrete part (output power MOSFET or the like) and a gain control amplifier called a linear amplifier is connected to a previous stage thereof. The linear amplifier and a bias circuit for supplying a bias current therefor are formed on one semiconductor chip as semiconductor integrated circuits.
A system has been generally configured such that a cellular phone makes a phone call while changing an output (transmission power) so as to adapt to a surrounding environment according to a power level instruction signal sent from a base station in accordance with a use environment and avoids interference with other cellular phones. A high-frequency power amplifier module corresponding to an output stage on the transmitting side of a cellular phone of, for example, a North American 900 MHz-band standard system, a GSM (Global System for Mobile Communication) or the like has a configuration wherein a gate bias voltage of an output power element is controlled so as to reach output power necessary for calling according to a control voltage VAPC outputted from an APC (Automatic Power Control) circuit.
Meanwhile, a cellular phone of a conventional GSM or DCS (Digital Cellular System) is generally configured such that a gain control amplifier selects gain stepwise. In a cellular phone of a CDMA (Code Division Multiple Access) system on the other hand, a gain control amplifier, particularly, an amplifier for controlling the level of a transmit signal needs to linearly control gain. To this end, a linear gain converting circuit has been used which supplies such a bias current as to linearly change the gain of the amplifier with respect to an output control voltage VAPC supplied from a baseband circuit or the like, to the amplifier.
It is necessary that the bias current outputted from the linear gain converting circuit changes exponentially with respect to the control voltage VAPC. Thus, a linear gain converting circuit might be conventionally used which comprises a bipolar transistor Qa, a constant voltage source VBB for supplying a base potential to the bipolar transistor Qa according to a control voltage VAPC, and an attenuating amplifier ABB such as shown in FIG. 8 by way of example. The attenuating amplifier ABB is used because a variable range of the control voltage VAPC is about 0V to about 2V whereas a variable range of the base voltage of the transistor Qa is low as in a range of 0.7V to 0.9V.